Many functions of modern devices in automotive, consumer and industrial applications, such as converting electrical energy and driving an electric motor or an electric machine, rely on semiconductor devices. For example, Insulated Gate Bipolar Transistors (IGBTs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) and diodes have been used for various applications including, but not limited to switches in power supplies and power converters.
Occasionally, a semiconductor device is equipped with means for carrying out a protective function, such as a short circuit turn-off function. To this end, the semiconductor device may be electrically coupled to a control circuit that controls operation of the semiconductor device in dependence of a semiconductor device temperature and/or in dependence of a semiconductor device load current that flows through the semiconductor device. For example, if the semiconductor device temperature and/or the semiconductor device load current exceeds a respective threshold value, the control circuit may react by turning off the semiconductor device, which causes the load current to be reduced to approximately zero.
In order to determine a load current, it is known that some of the emitter current of an IGBT can be directed separately via an auxiliary connection. In terms of magnitude, this current can be proportional to the main emitter current, i.e., the load current. A measurement signal can be evaluated by means of an external control circuit comprising, for example, a low-impedance resistance, and if applicable, subsequent circuit amplification and isolated signal transmission. For example, the voltage-drop across the low-impedance resistance is proportional to the main emitter current.
A temperature measurement may be implemented by means of a pn-junction (diode), the forward voltage-drop of which is dependent on the temperature and can be evaluated by using an external control circuit.
For determining a semiconductor device temperature and/or a semiconductor device load current, it is sometimes desirable to measure an electrical potential of a part of a semiconductor body region of the semiconductor device.
It is known to use a separated region of the semiconductor body region of the semiconductor device for determining said electrical potential, wherein the separated region is usually located within an edge area of the semiconductor device and, due to this location, not available for conducting the load current. Using such separated region for measurement purposes leads, therefore, to a loss of the area of this separated region of the device that otherwise would be available for conducting the load current, i.e., to loss of active semiconductor area. Further, since the separated region is separated from the remaining semiconductor body region that is used for load operation of the semiconductor device, signals generated within the separated region are not exactly indicative for the state of the semiconductor body region that is used for load operation of the device. Such possible inaccuracy of the measurement has to be taken into account by the control circuit, which may cause the control circuit to be rather complex.
According to DE 101 23 818 B4, a control circuit implements the protection function and is controlled by an electrically floating region that is located in a semiconductor body region of the semiconductor device. Further, the semiconductor device known from that publication contains a MOS transistor whose gate electrode is electrically connected to the electrically floating region or consists of the electrically floating region. For example, for implementing a short-circuit power cutoff, an electrical potential of a floating p-region of the semiconductor body region is used.